Radiant heating systems, such as those used to heat concrete or wood floors of residential and commercial buildings, typically employ hot water conveying copper pipe embedded within a concrete slab, or in sand beneath the slab thereby providing additional thermal mass. Heated water is circulated through the pipes to transfer thermal energy from the water to the concrete or sand, and in turn heat the space above the slab by radiation.
Heat transfer systems using copper pipe have several serious shortcomings. They are subject to corrosion, particularly by alkali in the concrete. The thermal expansion and contraction of the pipes together with the shifting and cracking of the concrete impose stresses which can cause leaks in the pipe. Those leaks are virtually impossible to repair without tearing up the floor.
Concrete has a low rate of heat transfer in comparison to copper. The use of low temperature water with copper pipe is inefficient and is not economically practical. Copper pipe is expensive and the cost of such systems becomes prohibitive unless relatively high water temperatures are employed.
An alternative to copper pipe is a thermoplastic pipe such as rigid or semi-flexible polyvinyl chloride pipe. Thermal expansion and contraction of the thermoplastic pipe is low. Since thermoplastic pipe can be expanded if necessary, freezing water which expands on becoming frozen cannot cause ruptures to the pipe. The elastic properties of the thermoplastic pipe also make it more resistant to damage caused by shifting or cracking of the concrete floor. The thermoplastic tubular system is low in initial cost and is particularly advantageous for efficient low-temperature heat transfer.
Five U.S. patents, a Canadian patent and a German patent disclose inventions which are relevant to radiant heat and chilled floor systems of general interest. These patents are listed below.
______________________________________ Inventor Issue Date ______________________________________ U.S. Pat. No. 3,893,507 MacCracken et al. July 8, 1975 4,032,177 Anderson June 28, 1977 4,269,172 Parker et al. May 26, 1981 4,779,673 Chiles et al. October 25, 1988 4,782,889 Bourne November 8, 1988 Canadian Zinn et al. November 3, 1981 Patent Number 1,111,839 German Von Dresky December 23, 1969 Patent Number 1,964,395 ______________________________________
In U.S. Pat. No. 4,269,172, Parker et al. disclose a solar hot-water heating system which is suitable for mounting on the roofs of buildings. The system includes manifolds 20 and 21, and triple tubes 18 and 22 (FIG. 2). The result is an arrangement of circulation ducting which has heat exchange benefits and reduces overall heat loss.
Chiles et al. in U.S. Pat. No. 4,779,673 disclose a heat exchanger construction which, in one embodiment, can be embedded in a concrete floor. The system includes tubing 20 connected to parallel manifolds 30 and 32 (see FIG. 2). There is not any heat exchange capacity between the adjacent tubes. Chiles et al. do not disclose units of triple abutting tubes.
Bourne in U.S. Pat. No. 4,782,889 discloses a low mass hydronic radiant floor heating system which includes a metal deck which has regularly spaced troughs therein. Tubing is placed in the troughs to distribute heat by circulating warm liquid through the tubing. In this arrangement the tubing is not embedded in the concrete. Bourne does not disclose counter current fluid flow through a triple abutting tube unit system.
MacCracken, in U.S. Pat. No. 3,893,507, discloses a grid system of single plastic tubes which is used to create and maintain an ice slab. The tubes are not intrinsically joined into triplets. The single tubes are joined at specified locations by clips. MacCracken does not disclose a unitary triple abutting tube combination with a unique tube-manifold connection system.
Anderson, in U.S. Pat. No. 4,032,177, discloses a compression fitting for a tubing system including a nut 31, double female thread fitting body 10, insert 30, and compression sleeve 23. The fitting is not specific to the radiant floor heating industry. The fitting is designed to secure a flexible tube to a metal fitting. The Anderson fitting is prone to causing damage to the flexible tubing because it is easy overtighten the nut and cause the rigid sleeve at the end away from the nut to bend against the tube and puncture the tube. Anderson does not disclose a resilient sleeve which bears against an area of the tubing and yields when the nut is over-tightened, thereby avoiding puncturing or weakening the tube.
In Canadian Patent No. 1,111,839, Zinn et al. disclose a heat exchanger in the form of a mat having a plurality of fluid conducting tubes arranged parallel to one another and joined by connecting webs. More particularly, Zinn et al. disclose a heat exchanger for radiant floor use having six parallel fluid-conducting tubes of elastomeric material. The tubes are formed in an elongated mat with flexible webs separating and connecting adjacent tubes. Opposite end portions of all of the tubes remote from the central mat section are free of the webs and are connected to respective hollow manifolds through respective holes in the manifold walls. The tubes or mats are formed integrally by extrusion of an elastomeric material such as synthetic rubber and particularly EPDM (polymerized ethylenepropylenediene monomer or terpolymer). A problem with plastics, and EPDM in particular, is that when hot water first enters such tubes, the hot water forms a soft spot adjacent the inlet and consequently in situations where the tube is connected to a simple solid metal nipple or fitting, and the water is under pressure, the tube tends over time to work free from the nipple or fitting.
Von Dresky, in German Patent No. 1,964,395, discloses a square cross-section, interlocking tube system for a floor heating system. Von Dresky does not disclose a circular cross-section abutting triple tube unit which can be readily split apart, or maintained as a unit. Von Dresky does not show counter current flow or a dual manifold system, or a unique tube gripping fitting.